Avalanche Forecast

Archived

Mar 8th, 2017–Mar 9th, 2017

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Lizard-Flathead.

The best and safest riding will likely be found in sheltered, lower elevation terrain.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Thursday: 2-4cm of new snow / Light southwest winds / Alpine temperature of -10Thursday night and Friday: up to 25cm of new snow / Strong to extreme southwest winds / Alpine temperature of -7Saturday: Mix of sun and cloud / Moderate southwest winds / Alpine temperature of -3 / Freezing level at 1500m

Avalanche Summary

In the past two days at treeline and alpine, natural storm slab and loose dry avalanches to Size 2 have been reported on south through northeast aspects. Cornices are large and remain easy to trigger. A great image from Sunday illustrates just how surprising the results can be. Click here for details. Natural activity is expected to taper off on Thursday, but storm slabs are expected to remain sensitive to human triggering. Looking forward, natural storm slab activity is expected to ramp-up again in response to new snow and wind on Thursday night and Friday

Snowpack Summary

Another day, another 10-15 cm of snow falling: The weekly total now stands at roughly 130 cm. At times, strong southwest winds have extensively redistributed the snow and formed large brittle cornices. Over the weekend the new snow came in "upside down" (heavier, denser snow over lighter snow) and is rapidly settling into a slab which sits over a variety of old surfaces including surface hoar, facets, stiff wind slabs, sun crusts, and a rain crust below 1900 m.Isolated basal weaknesses may still exist in shallow snowpack areas and appear to isolated to north-northeast aspects in the alpine.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.